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[aprssig] APRS Digipeter Design Questions

Tapio Sokura oh2kku at iki.fi
Fri Apr 29 16:02:37 UTC 2005


Curt, WE7U wrote:
> Due to Mic-E protocol you also need to include the DEST callsign
> field, as that is part of your location.  That means you need
> SRC/DEST/INFO.

And to be more exact, I guess you'd want to leave the destination SSID 
out of the checksum, because it can change when a mic-e packet is 
digipeated. OTOH, most digipeaters don't seem to implement destination 
SSID digipeating, so it's not that big of a deal in practice.

If one wanted to do a bit fancier duplicate checking, I guess you could 
also check the body. If the body contains a third party packet, use the 
third party sender/target/body information for duplicate checking. And 
also ignore trailing crs, lfs and spaces in packet bodies. I guess a 
plain digipeater can ignore these things, but an igate should do these 
checks before deciding to gate packets.

Not really relevant to duplicate checking, but checking the digipeater 
chain length might be a useful feature as well. I.e. if the packet has 
already been digipeated n times, don't digipeat it again (or digipeat, 
but truncate the rest of the path).

   Tapio




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